The effects of pinealectomy and blinding on the circadian locomotor activity rhythm in the Japanese newt,Cynops pyrrhogaster

We examined the effects of pinealectomy and blinding (bilateral ocular enucleation) on the circadian locomotor activity rhythm in the Japanese newt, Cynops pyrrhogaster. The pinealectomized newts were entrained to a light-dark cycle of 12 h light and 12 h darkness. After transfer to constant darkness they showed residual rhythmicity for at least several days which was gradually disrupted in prolonged constant darkness. Blinded newts were also entrained to a 12 h light/12 h dark cycle. In subsequent constant darkness they showed free-running rhythms of locomotor activity. However, the freerunning periods noticeably increased compared with those observed in the previous period of constant darkness before blinding. In blinded newts entrained to the light/dark cycle the activity rhythms were gradually disrupted after pinealectomy even in the presence of the light/dark cycle. These results suggest that both the pineal and the eyes are involved in the newt's circadian system, and also suggest that the pineal of the newt acts as an extraretinal photoreceptor which mediates the entrainment of the locomotor activity rhythm.Abbreviations circadian period - DD constant darkness - LD cycle, light-dark cycle - LD 12:12 light-dark cycle of 12 h light and 12 h darkness     

Circadian rhythm of a TCA cycle enzyme is apparently regulated at the translational level in the dinoflagellate Lingulodinium polyedrum

Previously, the authors have reported that intracellular amounts of several metabolic-related enzymes from the photosynthetic dinoflagellate Lingulodinium polyedrum(formerly Gonyaulax polyedra) showed a daily rhythm under a 12:12 h LD cycle. This led the authors to hypothesize that a circadian clock controls metabolism, including the tricarboxylic acid (TCA) cycle. In this study, the authors investigated daily changes in the levels of mRNA, protein, and enzyme activity of several metabolic enzymes during 12:12 h LD, 8:16 h LD, and constant light conditions. The NADP-dependent isocitrate dehydrogenase (NADPICDH) in the TCA cycle exhibited circadian changes of protein abundance and enzyme activity under all conditions, whereas its mRNA level remained constant throughout the cycle. These results indicate that the rhythm of NADPICDH is regulated by a circadian control of protein synthesis or modification rather than by message levels and suggest that the TCA cycle may be controlled by the circadian clock system.     

Phase of the circadian clock is accurately transferred from mother to daughter cells in the dinoflagellate Gonyaulax polyedra.

In the first cycle following transfer from a 12 h light-12 h dark cycle (LD12:12) to constant darkness (DD), the standard deviation in circadian phase among individual clocks in populations of Gonyaulax polyedra is approximately 60 min. When a culture is transferred to constant light conditions (LL) from an LD 12:12 cycle, the standard deviation increases in the first 2-3 d, but then remains unchanged, suggesting a lack of observable desynchronization in LL after the transient period. The synchrony in a cell population is preserved even after several cell divisions. The results indicate that variations in period among cells are small, that the period of an individual clock does not fluctuate randomly from day to day, and that the circadian phase of a mother cell is faithfully passed to the clocks of the daughter cells.     

The influence of light on cone disk shedding in the lizard, Sceloporus occidentalis

The lizard, Sceloporus occidentalis has an all-cone retina. In lizards maintained on a 12-h light:12-h dark (12L:12D) cycle, a burst of cone outer segment (COS) shedding occurs 2 h after light offset (1400 h circadian time) (Young, R.W., 1977, J. Ultrastruct. Res. 61:172-72). In this investigation, we studied the effect of different lighting regimes on the pattern of cone disk shedding in this species. When lizards entrained to a 12L:12D cycle are kept in constant darkness (DD), the shedding peak is advanced approximately 2 h and the magnitude of shedding is reduced to 30% of control. COS increased in mean length from 12 micron in controls to 14 micron after one cycle in DD and maintained this length during a second cycle in DD. In constant light (LL), disk shedding was damped to approximately 10% of control values. Shedding synchrony in LL was also perturbed and therefore cyclic shedding bursts could not be distinguished. During LL there was a much larger increase in COS mean length than in DD. After one cycle of LL, COS length was 15 micron and after two cycles COS length exceeded 17 micron. When lizards entrained to 12L:12D are shifted to a 6L:18D regimen, the first shedding cycle is biphasic. The first peak of 5% shedding occurs 2 h after light offset whereas a second larger peak (13%) occurs according to the entrained schedule (1400 h). This manipulation separates out a dark-triggered and circadian shedding component, which is normally superimposed in lizards entrained to a 12L:12D cycle. When entrained lizards are placed in 36 h of LL followed by light offset, the peak shedding response after light offset is double the control response (53% vs. 27%). After 30 h of LL (lights off 90 degrees out of phase), there is a biphasic shedding response similar to the 6L:18D regimen although this time the dark-triggered shedding component is greater in magnitude then the circadian component. COS turnover is estimated by extrapolating from COS mean length increases during LL. From this method we obtained a 2.7-micron increase in COS length during each day in LL. If COS growth is not augmented during LL, this would yield a 4-5-d turnover time for the average 12.5-micron COS.     

Nocturnal activity in a diurnal rodent (Arvicanthis niloticus): the importance of masking

It is known that day-active Nile grass rats, Arvicanthis niloticus, increase the amount of activity in the night relative to that in the day when provided with running wheels. This was confirmed in the present study. Animals without a wheel displayed 69.0% of their general activity in the L phase of a 12:12 h light-dark cycle; animals provided with wheels had only 48.6% of their wheel revolutions in the light. The contribution of direct (masking) responses to light to the increased nocturnality of animals with wheels was examined in two experiments. In experiment 1, masking was tested by exposing the animals to repeated cycles of 30 min of entraining light and 30 min of a different, usually dimmer light, during the L phase of a 12:12 h light-dark cycle. For animals with wheels, there was more running during the 30-min pulses of dim light or darkness than during the 30-min periods of entraining light. In contrast, for animals without wheels, there was more general activity during the 30-min periods of entraining light than during the 30-min pulses of dim light or darkness. In experiment 2, the animals were first exposed to a 12:12 h light-dark cycle and then put on a 1:10:1:12 h LDLD skeleton photoperiod. Animals with wheels increased their running during the subjective day of the skeleton photoperiod compared to that in the actual day of the 12:12 h light-dark cycle. Animals without wheels showed similar levels of general activity during the subjective day of the skeleton photoperiod and the actual day of the 12:12 h cycle. These experiments demonstrate that when Nile rats have running wheels, their increased nocturnal activity is associated with an increased suppression of locomotion in direct response to light. It is possible that changes in masking responses to light may be an essential and integral component of switching between diurnal and nocturnal activity profiles.     

Circadian Rhythm in Pineal N-Acetyltransferase Activity: Rapid Phase Reversal and Response to Shorter than 24-Hour Cycles (IV)

N-Acetyltransferase (NAT) is an enzyme whose rhythmic activity in the pineal gland and retina is responsible for circadian rhythms in melatonin. The NAT activity rhythm has circadian properties such as persistence in constant conditions and precise control by light and dark. Experiments are reported in which chicks (Gallus domesticus), raised for 3 weeks in 12 h of light alternating with 12 h of dark (LD12:12), were exposed to 1-3 days of light-dark treatments during which NAT activity was measured in their pineal glands. (a) In LD12:12, NAT activity rose from less than 4.5 nmol/pineal gland/h during the light-time to 25-50 nmol/pineal gland/h in the dark-time. Constant light (LL) attenuated the amplitude of the NAT activity rhythm to 26-45% of the NAT activity cycle in LD12:12 during the first 24 h. (b) The timing of the increase in NAT activity was reset by the first full LD12:12 cycle following a 12-h phase shift of the LD12:12 cycle (a procedure that reversed the times of light and dark by imposition of either 24 h of light or dark). This result satisfies one of the criteria for NAT to be considered part of a circadian driving oscillator. (c) In less than 24-h cycles [2 h of light in alternation with 2 h of dark (LD2:2), 4 h of light in alternation with 4 h of dark (LD4:4), and 6 h of light in alternation with 6 h of dark (LD6:6)], NAT activity rose in the dark during the chicks' previously scheduled dark-time but not the previously scheduled light-time of LD12:12. In a cycle where 8 h of light alternated with 8 h of dark (LD8:8), NAT activity rose in both 8-h dark periods, even though the second one fell in the light-time of the prior LD12:12 schedule.(ABSTRACT TRUNCATED AT 250 WORDS)     

A circadian rhythm of thermal preference in the ant Camponotus mus: masking and entrainment by temperature cycles

Abstract. Along a stable temperature gradient and under a LD 12:12 h cycle, nurse workers of the ant Camponotus mus Roger 1863 (Hymenoptera: Formicidae) select for the brood two different temperatures daily: 30.8°C at the middle of the light period (circadian phase = 90°), and 27.5°C 8 h later, during the dark period (circadian phase = 210°), this rhythm being of endogenous nature.When a 24 h temperature cycle was superimposed along the thermal gradient, so that the immobile brood experienced a temperature transition as they receive when translocated by nurses (8 h at 30.8°C and 16 h at 27.5°C), no brood translocations occurred.The thermal cycle masked the rhythm of brood translocation when temperature fitted the daily pattern expected by nurses.When the same temperature cycle was presented with a phase-advance, nurses did not tolerate the early thermal increase and removed the brood as temperature rose.However, when workers experienced this new phase relationship between light and temperature cycles for more than 10 days, brood translocations were suppressed.Records under constant conditions of light and temperature indicated that the overt rhythm was locked-on to the expected early increase in temperature, so that the temperature cycle dominated over the LD cycle in resetting brood-carrying activity.     

Influence of experimental illumination and seasonal variation on crossbreeding mating in the snail Biomphalaria glabrata

The crossbreeding activities of the Schistosoma mansoni vector snail Biomphalaria glabrata were counted in a laboratory aquarium throughout the year under two regimes of 12h light: 12h dark from 7 A. M. to 10 P. M. Mating increased significantly in Autumn and Winter and just missed a significant inverse correlation with temperature and a direct one with locomotion. Other similar experiments were carried out to compare mating under various illumination conditions in complete daily cycle measurements. Mating counts decreased under the regimes which submitted snail to a total exposure of 12h light and 12h dark during a daily cycle in the following sequence: 12h light:12h dark alternating hourly with light gradient, 12h light:12h dark, 1h light:1h dark and 12h dark:12h light. Under two constant illuminations, the mating scored less than under the previous conditions, except under 12h dark:12h light. Under darkness the mating count was lower than under light conditions. There was no way to differentiate the night and day rhythms of mating on different days in each regime, except for mating under 12h light:12h dark alternating with light gradient, constant dark and 12h dark:12h light conditions. Mating increased in certain light and temperature conditions, in which the intensities should have an optimum value.     

Photic entrainment of circadian activity patterns in the tropical labrid fish Halichoeres chrysus

Yellow wrasses (Halichoeres chrysus) show clear daily activity patterns. The fish hide in the substrate at (subjective) night, during the distinct rest phase. Initial entrainment in a 12h:12h light-dark (12:12 LD) cycle (mean period 24.02h, SD 0.27h, n = 16 was followed by a free run (mean period 24.42h, SD 1.33h) after transition into constant dim light conditions. Light pulses of a comparable intensity as used in the light part of the LD cycles did not result in significant phase shifts of the free-running rhythm in constant darkness. Application of much brighter 3h light pulses resulted in a phase-response curve (PRC) for a fish species, with pronounced phase advances during late subjective night. The PRCs differed from those mainly obtained in other vertebrate taxa by the absence of significant phase delays in the early subjective night. At that circadian phase, significant tonic effects of the light pulses caused a shortening of the circadian period length. Entrainment to skeleton photoperiods of 1:11 LD was observed in five of six wrasses exposed, also after a 3h phase advance of this LD cycle. Subsequently, a 1:11.25 LD cycle resulted in entrainment in four of the six fish. It is suggested that the expression of the circadian system in fish can be interpreted as a functional response to a weak natural zeitgeber, as present in the marine environment. This response allows photic entrainment as described here in the yellow wrasse. (Chronobiology International, 17(5), 613-622, 2000)     

Changes in the Productivity and Nuclear Divisions in Synchronous Chlorella and Circadian Rhythm

Circadian rhythmic changes of cell production were found atthe end of a test cycle (LD 14 : 10 h) and the synthetic tendenciesduring the test cycle were examined. The rates but not the durationof syntheses of chlorophyll, DNA and soluble protein rhythmicallychanged with additional waiting time in the dark after a growthcycle (LD 14 : 10). Changes in the rates of RNA and total proteinsynthesis were apparent only during the first 9 h in the lightphase of the test cycle. However, the rate of carbohydrate synthesisduring the test cycle was completely different; an exponentialpattern was observed in cells with 0 and 24 h waiting times,but a sigmoid one in cells with 12 h waiting time. Nuclear divisions(into 16 or even more) followed DNA synthesis. Cells with 12h waiting time remained longer in each multinuclear phase (demonstratedby the 2 and 8 states) and showed extremely lowered productivity(ca. 50% only). ¹Department of Botany, National Chung Hsing University, Taichung,Taiwan, Republic of China. (Received May 14, 1985; Accepted June 14, 1986)     

Light regulation of the cell cycle in Euglena gracilis bacillaris

We have studied the light regulation of the cell division cycle in the photosynthetic alga Euglena gracilis bacillaris. Euglena grown under phototrophic conditions are easily synchronized to a 12 h light-12 h dark regime. By inoculating stationary phase, nondividing cells into fresh media and exposing the diluted cells to either light or darkness, we have determined that initiation of DNA synthesis for the cell division cycle is light dependent. By varying the length of time in light to which synchronized cells are exposed, we have shown that commitment to the cell cycle requires exposure to more than 6 h of light. We propose that this is to allow the accumulation, through photosynthetic electron transport, of an initiating factor that will enable DNA synthesis to begin. Flow cytometry analysis also shows that once cells are committed to the cell cycle, they complete the cycle in the dark, so mitosis is a light-independent step.     

Effect of sunlight on the survival of Salmonella on surfaces

AIMS: To investigate the effect of simulated full-spectrum tropical sunlight on the survival of Salmonella in droplets on surfaces. MATERIALS AND RESULTS: The survival on surfaces of three Zambian strains of Salmonella enterica serovars Enteritidis and Heidelberg was compared with that of a strain of S. enterica serovar Enteritidis phage type (PT) 4 with known characteristics which had been isolated from poultry in the UK. Samples were taken from surfaces every hour for 3 h and after 24 h exposure in either dark or 12 h light/12 h dark cycle conditions. Differences were analysed for significance using a one-way analysis of variance (anova). Results show that there were a significantly higher number of cells surviving on surfaces after 24 h in the dark when compared with populations exposed to a 12 h light/12 h dark cycle. Significantly more cells also survived exposure to sunlight under dirty than clean conditions. CONCLUSIONS: Exposure to sunlight results in a significant decrease in numbers of Salmonella on surfaces. SIGNIFICANCE AND IMPACT OF THE STUDY: Under field conditions exposure of contaminated surfaces to sunlight could be used in place of chemical methods of control as a cheaper way to reduce Salmonella contamination of surfaces.     

Determination of effective light pulse and classical Bünsow experiment in the larval diapause of the Indian meal moth Plodia interpunctella

Plodia interpunctella Hübner (Lepidoptera: Pyralidae) comprises a model insect to analyse the photoperiodic time‐measuring system controlling its larval diapause. In the present study, the effective length of light pulse in night interruption experiments is determined at 25 °C. Various lengths of light pulse are tested by inserting them at the midnight of an LD 12 : 12 h photoperiod. When the light pulse is 15 or 30 min, the incidence of diapause is 86%. To inhibit the induction of diapause effectively, a light pulse of 1.75–2 h is needed. The incidence of diapause is 12% under an LD 12 : 5 : 2 : 5 h photoperiod. To determine the precise role of the light pulse, 2‐h light pulses placed at the midnight of an LD 12 : 12 h photoperiod are disrupted systematically by darkness. When a 2‐h light pulse is disrupted by 15 min of darkness, diapause is generally prevented (< 29%) regardless of the temporal position of darkness. Longer disruption by darkness induces diapause moderately (37–67%). A Bünsow experiment is also conducted at 25 and 20 °C, in which the main photophase of 12 h of light is combined with 24–72‐h scotophases scanned by a 2‐h light pulse. The photoperiodic cycle length tested, therefore, varies in the range 36–84 h. In each cycle length, the incidence of diapause fluctuates as the light pulse moves toward dawn. However, no regular and circadian changes in the percentage diapause are observed in relation to diapause determination.     

Ecdysteroids influence the circadian system timing ecdysis in the insectRhodnius prolixus (Hemiptera)

Summary 20-hydroxyecdysone (20HE) injections induced transient delays in the time of ecdysis inRhodnius prolixus reared in L/D cycles. Sustained phase delays in the ecdysis rhythm were revealed by transfer to constant dark during the scotophase following 20HE injection. The magnitude of the phase delays depended on the time in the L/D cycle at which 20HE was injected with major delays occurring at times when the endogenous titre is declining. Therefore the increases and decreases in the endogenous titre which are themselves timed in a circadian fashion may be involved in phase setting the ecdysis rhythm to the environmental cycle. Populations maintained in LL which are arrhythmic with respect to both ecdysteroid titres and ecdysis, can be induced to display gated ecdysis by injection of either 20HE or antiserum to ecdysteroids. Multiple injections of 20HE or antiserum are capable of inducing an ecdysis rhythm whose period (22.3 h) and gate location are very similar to that produced by altering the environmental cycle. Therefore manipulations of the endogenous titre of ecdysteroids can mimic the effects of L/D cycles on the timing of ecdysis. Ecdysis inRhodnius may therefore be timed at least partially as a result of circadian timing of the ecdysteroid titre.Abbreviations AZT Arbitrary Zeitgeber Time - DD constant darkness - LL constant light - L/D 24 h light dark cycle - 12L/12D 12 h of light 12 h of dark - 20HE 20-hydroxyecdysone     

Microbiochemical investiagation on diurnal rhythmic changes of the activities of the lactate dehydrogenase in the periportal and perivenous zones of the acinus of the rat liver

Summary Activities of the lactate dehydrogenase within the periportal zone and within the perivenous zone in the first layer of hepatocytes adjacent to terminal hepatic venules and the remainder of the perivenous parenchyma of the liver acinus were measured using a Lowry technique during a full 24-h cycle (08.00-08.00) in untreated adult male Wistar rats kept under 12 h of light and 12 h of darkness, scotophase 18.25-06.25. In all three regions studied a broad first maximum was recorded between 10.00 and 22.00 with the peak value at 16.00 and a high and narrow peak at 24.00. Zonal and intrazonal heterogeneity of the lactate dehydrogenase were retained during the full day and night cycle. The regions displayed individual dynamic changes in enzyme activity.Supported by the Deutsche Forschungsgemeinschaft (Hi 318/21)     

The effect of cell cycle on GFPuv gene expression in the baculovirus expression system.

The effects of cell cycle on recombinant protein production and infection yield in the baculovirus-insect cell expression system (BES) were investigated. When, at any cell cycle phase, the host cell was infected by baculovirus, the cell cycle was finally arrested at the S or G(2)/M phase with 4n DNA. In the case of G(1) or S phase-infection, cell cycle of virus-infected cells began to be arrested at S phase from 8 h post-infection or at G(2)/M phase from 4 h post-infection, respectively; while, in the case of M phase-infection, cell cycle was arrested at S phase after 12 h post-infection. When the host cell was infected at the G(1) phase, average intracellular GFPuv fluorescence intensity was 1.3-fold higher than that at G(2)/M phase at 24 h post-infection. The GFPuv expression corresponded to the profile of the G(1) cell cycle in the BES. Infection yield was measured by detection of intracellular DNA binding protein using immunohistochemical method within 7 h post-infection. The infection yield at G(1) or S phase-infection was 1.5-1.8-fold higher than that at G(2)/M phase-infection.     

Effect of exogenous gonadotrophin (PMSG) on the antral follicle population in the sheep.

Follicles were obtained from the ovaries of four groups of 15 ewes. Ewes in the control group were ovariectomized on the 12th day of the oestrous cycle. The other ewes were all given PMSG on the 12th day of the cycle; some were ovariectomized 24 or 40 h later, the others were given prostaglandin followed by hCG and were ovariectomized 6 or 12 h after the hCG injection. All follicles greater than 2 mm in diameter were measured and examined macroscopically for signs of atresia. Some were subjected to detailed morphological examination, the pattern of steroid secretion was determined in others. All the evidence from these three approaches suggested that, in vivo, reversal of the atretic process ('rescue') plays no part in the increase in the number of follicles observed following administration of PMSG.     

Diurnal changes in the fraction of 3-hydroxy-3-methylglutaryl-CoA reductase in the active form in rat liver microsomal fractions.

'Initial' and 'total' activities of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) were measured in cold-clamped samples of liver from rats at 2h intervals throughout the 24h light/dark cycle. Initial activities were obtained in microsomes (microsomal fractions) isolated and assayed in the presence of 100mM-KF, whereas 'total' activities were measured in microsomes prepared from the same homogenates but washed free of KF and incubated with exogenous partially purified rat liver protein phosphatase. The initial/total-activity ratio for HMG-CoA reductase underwent a diurnal cycle, which had a nadir 4h into the light phase (when initial activity was 28% of total activity) and a peak 12h later, i.e. 4h into the dark phase (when initial activity was 80% of total activity). These low and high points of the cycle were separated by gradual steady changes in the ratio. The characteristics of this diurnal cycle were different from those of the cycle observed for total activity, which had a plateau of high activity between 2 and 10h into the dark cycle preceded and succeeded by a very rapid increase and decrease, respectively, in the total activity of HMG-CoA reductase. The combination of the two cycles resulted in the dampening of the resultant cycle for the initial or effective activity of HMG-CoA reductase, such that the changes in initial activity around the beginning and and end of the dark phase were more gradual than would otherwise have been the case if the initial/total-activity ratio for HMG-CoA reductase were constant throughout the diurnal cycle. The physiological implications of the observed diurnal variation in the fraction of hepatic HMG-CoA reductase in the active form are discussed.